Crankshaft bearing system

ABSTRACT

The subject invention refers to a crankshaft bearing system (1) for an internal combustion engine, in which the engine&#39;s crankshaft (15) is mounted in permanently lubricated sealed bearings (2, 3), usually ball bearings (2, 3), and the engine&#39;s crankcase seals (4, 5) are located inside each bearing (2, 3), i.e. between the bearing (2, 3) and the crankshaft assembly (6) with piston rod (7) and counterweights (8, 9), and a draining duct (11) is arranged in the crankshaft so that it leads from a space (12) between one of the crankcase seals (4, 5) and adjacent bearing out to the surrounding air.

TECHNICAL FIELD

The subject invention refers to a crankshaft bearing system for aninternal combustion engine.

BACKGROUND OF THE INVENTION

According to tradition internal combustion engines have crankshaftbearings, which are lubricated from the crankcase, for instance byoil-splash lubrication. Regarding crankcase scavenged engines thebearings are usually lubricated by the fuel-oil-mixture in thecrankcase. The crankcase seals are located outside the bearings. Thismeans that the bearings are subjected to dirt and residual combustiondeposits which could shorten the lifetime. Also, the design of thebearings can affect the crankshaft's mechanical stability regardingbending vibrations. High-speed engines, such as two-stroke engines forchainsaws etc., can achieve, in point of bending vibrations, a criticalrange of speed. Regarding crankcase scavenged engines also the crankcasecompression is affected by the design of the bearings and seals, andconsequently the engine power.

PURPOSE OF THE INVENTION

The purpose of the subject invention is to substantially reduce theabove outlined problems, and to achieve advantages in many respects.

SUMMARY OF THE INVENTION

The above mentioned purpose is achieved in that the crankshaft bearingsystem in accordance with the invention having the characteristicsappearing from the appended claims.

The crankshaft bearing system in accordance with the invention is thusessentially characterized in that the engine's crankshaft is mounted inpermanentely lubricated sealed bearings, usually ball bearings, and inthat the engine's crankcase. seals are located inside each bearing, i.e.between the bearing and the crankshaft assembly with piston rod andcounterweights. On a conventional crankshaft the seals are insteadlocated outside each bearing. The new location inside the bearingresults in many advantages. The crankshaft becomes stiffer and itsharmonic frequency of bending will increase, and in this manner comesmore far away from the range of engine speed. The crankcase compressionwill increase. The bearings are sealed and permanentely lubricated,usually by grease lubrication. Hereby the bearings will not be subjectedto dirt or combustion deposits, which could shorten the lifetime. Owingto this the lifetime will be longer, and/or smaller and lighter bearingscan be used. These and other characteristic features and advantages ofthe invention Will become more apparent from the following detaileddescription of various embodiments with the support of the annexeddrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in closer detail in the following by wayof various embodiments thereof with reference to the accompanyingdrawing, in which the same numbers in the different figures state oneanother's corresponding parts.

FIG. 1 illustrates schematically a crankshaft bearing in accordance withthe invention seen from the side.

FIG. 2 illustrates enlarged a part of the crankshaft, according to FIG.1, with bearing and crankshaft seal as well as a draining duct.

In FIG. 1 numeral 1 designates a crankshaft bearing system or acrankshaft arrangement in accordance with the invention. A crankshaft 15is mounted in two roller bearings 2, 3, usually ball bearings. Theengine's crankcase seals 4, 5 are located inside each bearing 2, 3, i.e.between the bearing and the crankshaft assembly 6 with piston rod 7 andcounterweights 8, 9. The design of the crankshaft assembly is entirelyconventional and will therefore not be further described.

FIG. 2 shows a partial enlargement of the crankshaft 15 and the bearing2. As appears from the figure the bearing 2 is externally enclosed in abearing holder 10. The bearing holder 10 comprises two parts, one innersolid part 16 and one outer elastic part 17. The solid part 16 isusually composed of a metallic part, usually a stamped tin cup. It hasan inner diameter of a size adapted to give a suitable grip towards thebearing 2. The solid part 16 also goes down along the side of thebearing. This is advantageous considering the fastening and localizationof the seal 4. In this case the seal 4 and the elastic part 17 areintegrated into one part, but they could also be composed of twoseparate parts, each part to be mounted to the solid part 16. Theelastic part 17 could for instance be composed of a coating along theouter periphery of the solid part 16. The purpose with the solid partis, on the one hand to achieve an elastic mounting of the bearings, andon the other hand to achieve a sealing around the periphery of thebearings. By the elastic mounting of the bearings a more quiet engineoperation can be achieved and consequently less vibrations and noise.Furthermore tolerances and irregularities will be taken care of. Thebearing holder 10 can be mounted either directly into each crankcaseside or into an intermediate sleeve.

In reality this sleeve is just a metal cover to be used in certainapplications.

As appears from the FIGS. 1 and 2 the bearing is pressed on thecrankshaft 15 against a shoulder 18 on the shaft. Consequently, theshaft's diameter is larger than the bearing's inner diameter inside eachbearing 2, 3, i.e. between the bearing and the crankshaft assembly. Inthe shown cross-sectional view in FIG. 2 a draining duct 11 extendsthrough the shoulder 18 and under the bearing. The draining duct 11 isthus embodied as a depression in the crankshaft surface, said depressionextends under the inner ring 13, 14 of the bearing, so that the drainingduct debouches on each side of the inner ring. Owing to this the sealsof the sealed ball bearing or roller bearing will not be subjected topressure, which they normally don't tolerate. The draining duct 11 isthus so arranged that it leads from a space 12 between one of thecrankcase gaskets 4, 5 and the adjacent bearing out to the surroundingair. The draining duct could also be embodied in the solid part 16 or inthe elastic part 17, so that communication with the surrounding aircould be created along the outside of the bearing instead of along itsinside. This could be relevant especially regarding multi-cylinderengines. In this case draining ducts, from both sides of the bearing,could be drained through ajoining duct in the crankcase. However, thedraining duct could also be composed of a radial hole in the crankshaft,said hole meets with an axially extending centre hole in the crankshaft.The radial hole can be in contact with the surrounding air, eitherthrough another radial hole, or otherwise the centre hole could extendall the way out to the end of the crankshaft. This solution can also beapplicable for multi-cylinder engines. However, normally the inventionis of greatest advantage for a one-cylinder engine. Especially for acrankcase scavenged engine the invention means a great deal ofadvantages. Such an engine has a lubricating system independent ofposition and handling, and is normally therefore used for portableworking tools, such as chain saws.

Thus, the most characteristic feature of the invention is that each seal4, 5 respectively is located inside its respective one of bearing 2, 3,which is permanentely lubricated. In comparison with a conventionalcrankshaft bearing system, where the gasket is located outside thebearing, which is not sealed and permanentely lubricated, this means alot of advantages. Firstly it means that the bearings 2, 3 respectivelyare located more far out from the crankshaft assembly 6. Hereby thebearing base has increased and the overhang at each shaft end has beenreduced. Heavy details such as flywheel and clutch are located at eachshaft end. The widening of the bearing base means that the crankshaft'sbending out is reduced and its bending harmonic frequency is increased,which is very positive. For, a problem is that these kind of engines arevery easily-speeded and under certain conditions they can thereforeachieve this critical speed. This is particularly true for two strokeengines. The shoulder 18 contributes to a stiffer shaft. Since eachbearing 2, 3 is located more far away from the crankshaft assembly 6,the thicker part with shoulders 18 will extend further towards the shaftends of the crankshaft 15. Like the widening of the bearing base thiscontributes to a stiffer crankshaft. By these both cooperatingstiffening factors also a comparatively small transfer of each bearingcan provide a great stiffening effect, and thereby an utterly desirableincrease of the range of speed where the bending resonance arises.Operation in this range of speed will soon result in engine troubles. Ifthe speed range is moved to a higher level, i.e. with a larger speedmargin in relation to the engine's normal running speed, running in thiscritical range can be eliminated or essentially reduced.

Furthermore this crankshaft bearing system means that the crankcasevolume will be reduced due to the fact that the air volume in thebearings is eliminated. This is of course due to the fact that the seals4, 5 are located inside the bearings instead of outside. The reducedcrankcase volume means that the crankcase compression will increase.This results in a more effective crankcase scavenging which isadvantageous regarding emissions etc. In case the invention is used incombination with other measures taken in order to increase the crankcasecompression, this effect will be particularly large. One such step toincrease the crankcase compression is to provide the counterweights 8,9, i.e. the so called balances, with filling material of low density, sothat as large part of the crankcase volume as possible will be filledout. Normally the counterweights 8, 9 have not that kind of fillingmaterial. The fillings are designed so that each part 8, 9 is includedin a circular top-filled disc. The invention can also be used for anengine with an single-side joumalled crankshaft, i.e. a crankshaftjournalled only on one side of the crankshaft assembly. Naturally, whathas been mentioned above, is also applicable to the bearing located mostadjacent the crankshaft assembly and its related seal.

What is claimed is:
 1. A crankshaft bearing system (1) for an internalcombustion engine, wherein a crankshaft (15) is mounted in single-doselubricated roller bearings (2, 3) and crankcase gaskets (4, 5) arelocated inside each bearing (2, 3), said gaskets being between thebearing (2, 3) and the crankshaft assembly (6) with piston rod (7) andcounterweights (8, 9), wherein one draining duct (11) is arranged in thecrankshaft so that said duct leads from a space (12) between one of thecrankcase seals (4, 5) and adjacent bearing out to the surrounding air.2. A crankshaft bearing system (1) in accordance with claim 1, wherein adiameter of the crankshaft (15) is larger than an inner diameter of eachbearing (2, 3).
 3. A crankshaft bearing system (1) in accordance withclaim 1, wherein the internal combustion engine is a one-cylinderengine.
 4. A crankshaft bearing system (1) in accordance with claim 1,wherein the internal combustion engine is a crankcase scavenged engineintended for portable working tools.
 5. A crankshaft bearing system (1)according to claim 1, wherein at least one of the bearings (2, 3) isexternally enclosed in a bearing holder (10).
 6. A crankshaft bearingsystem (1) in accordance with claim 5, wherein a diameter of thecrankshaft (15) is larger than an inner diameter of each bearing (2, 3).7. A crankshaft bearing system (1) in accordance with claim 5, whereinthe internal combustion engine is a one-cylinder engine.
 8. A crankshaftbearing system (1) in accordance with claim 5, wherein the internalcombustion engine is a crankcase scavenged engine intended for portableworking tools.
 9. A crankshaft bearing system (1) according to claim 5,wherein at least one of the crankcase seals (4, 5) is mounted into, orintegrated with the bearing holder.
 10. A crankshaft bearing system (1)in accordance with claim 9, wherein a diameter of the crankshaft (15) islarger than an inner diameter of each bearing (2, 3).
 11. A crankshaftbearing system (1) in accordance with claim 9, wherein the internalcombustion engine is a one-cylinder engine.
 12. A crankshaft bearingsystem (1) in accordance with claim 9, wherein the internal combustionengine is a crankcase scavenged engine intended for portable workingtools.
 13. A crankshaft bearing system (1) according to claim 9, whereinthe draining duct (11) is a depression (11) in a surface of thecrankshaft (15), said depression extends under an inner ring (13, 14) ofthe bearing (2, 3), so that it debouches on each side of the inner ring(13, 14).
 14. A crankshaft bearing system (1) in accordance with claim13, wherein a diameter of the crankshaft (15) is larger than an innerdiameter of each bearing (2, 3).
 15. A crankshaft bearing system (1) inaccordance with claim 13, wherein the internal combustion engine is aone-cylinder engine.
 16. A crankshaft bearing system (1) in accordancewith claim 13, wherein the internal combustion engine is a crankcasescavenged engine intended for portable working tools.